Are there any advantages of bigger/smaller tiles
There are two considerations involved with tiled rendering:


There is some overhead when switching tiles. Larger tiles = fewer tiles = less switching = less extra processing time.
Smaller tiles render faster (which reduces the likelihood that one tile is left rendering at the end, leaving all the other processors idle *) 


You must find a balance between these two factors (In other words, you don't want all your processing time to be spent switching between tiles). The optimal tile size for you will probably be specific to your scene, hardware configuration, personal preferences (e.g. sacrificing a small amount of speed for larger/smaller tiles), etc.

See Best Tile Size for Blender Internal Renderer and Cycles for some examples.

* this assumes you have more then one processor/core in your system.